Modulation of electrolyte homeostasis by dietary nitrogen intake in growing goats

Abstract

In goats, the combination of dietary N and Ca reduction caused hypocalcaemia and further changes in Ca homeostasis. The aim of the present study was to characterise the effects of dietary N reduction under normocalcaemia on mineral and bone metabolism in young goats. Young male goats of the Saanen breed were fed a diet reduced in N (8 %) for about 7 weeks (ten animals per group) and were compared with goats fed with an adequate N (14 %) diet. When N intake was reduced in young goats, plasma urea concentrations as well as renal elimination of urea were reduced. This was inversely related to creatinine in plasma and urine, which increased during a dietary N reduction as a function of reduced renal activity to save urea during N scarcity. During this decrease in renal function, associated with declined insulin-like growth factor 1 concentrations, a reduction in calcidiol and calcitriol concentrations could be observed. Meanwhile, carboxyterminal cross-linked telopeptide of type I collagen values and activity of total alkaline phosphatase were both elevated, indicating some bone remodelling processes taking place during a reduced N diet in young goats. The concentrations of inorganic phosphate (P i ) and total Ca were changed in several body fluids, indicating that P i and Ca homeostasis was perturbed in goats fed a reduced N diet. Therefore, more research is needed to find the balance between reduction of environmental N pollution by reducing dietary N in ruminant feeding and maintaining the animal's health.

Modulation of aquaporin 2 expression in the kidney of young goats by changes in nitrogen intake

“…A detailed description of the study design, feeding system and animals has been described previously (Muscher et al 2011). Briefly, twenty male white Saanen goats, aged about 3 months were randomly divided into two feeding groups consisting of ten animals each.…”

“…Therefore, interplay of aquaporin water channels and urea transporters in the kidney may occur to maintain urea metabolism in times of N scarcity in young goats. about 92 % (Muscher et al 2011). In a former study, it could be shown that an N-reduced diet in young goats led to an upregulation of urea transporter UT-A1 mRNA expression in renal medulla (Starke et al 2012), assuming that this is an important mechanism for saving urea in times of N scarcity.…”

“…In monogastric animals, the CaR functions as a potential modulator of renal AQP2 expression (Bustamante et al 2008). In our previous studies, changes in Ca homeostasis like reduction in calcitriol concentrations occurred during dietary N reduction in young goats Muscher et al 2011). Different studies in monogastric animals showed contradictory results concerning the effect of calcitriol on CaR expression (Brown et al 1996;Rogers et al 1995).…”

“…A reduction in dietary N caused serious changes in urea metabolism and mineral homeostasis in young goats (Muscher et al , 2011Starke et al 2012). Therefore, it is hypothesised that the expression of renal AQPs and the CaR is modulated in young goats fed a reduced-N diet to support renal urea absorption by concentrating tubular fluid.…”

“…Water intake of individual goats was not monitored in the current study. However, there was no evidence that a reduced-N diet caused dehydration and therefore hypertonicity of the extracellular fluid because no changes of the haematocrit, plasma osmolarity, total plasma protein or albumin content were detected (Muscher et al 2011). Thus there was no evidence for haemoconcentration or haemodilution.…”